Sugru is a clay-like synthetic wondermaterial that can be easily shaped with your hands and hardens completely after 24 hours. You can use it to fix and modify anything. It's really cool in itself, but awesome when you combine it with powerful magnets.
I haven't tried their magnet kit yet, but I just fixed a bronze lamp last weekend using it and I was amazed at how well it worked. This magnet stuff is so ingeniously simple that watching it in action makes me smile.